The halo by halo missing baryon problem

Abstract

The global missing baryon problem - that the sum of observed baryons falls short of the number expected form BBN - is well known. In addition to this, there is also a local missing baryon problem that applies to individual dark matter halos. This halo by halo missing baryon problem is such that the observed mass fraction of baryons in individual galaxies falls short of the cosmic baryon fraction. This deficit is a strong function of circular velocity. I give an empirical estimate of this function, and note the presence of a critical scale of ~900 km/s therein. I also briefly review Omega_b from BBN, highlighting the persistent tension between lithium and the CMB, and discuss some pros and cons of individual galaxies and clusters of galaxies as potential reservoirs of dark baryons.

10 pages, review for IAU Symposium 244, Dark Galaxies & Lost Baryons

References in corpus (6)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• On the mass-to-light ratio of the local Galactic disc and the optical luminosity of the Galaxy
• A probable stellar solution to the cosmological lithium discrepancy
• The baryon fraction of LambdaCDM haloes
• From First Stars to the Spite Plateau: a Possible Reconciliation of Halo Stars Observations with Predictions from Big Bang Nucleosynthesis
• Revisiting the Baryon Fractions of Galaxy Clusters: A Comparison with WMAP 3-year Results